Spark plug



Nov. 21, 1939. A. A. KASARJIAN SPARK PLUG Sept 9' INVENTOR Patented Nov. 21, 1939 UNITED STATES PATENT OFFKZE] Application September 4 Claims.

This invention relates to spark plugs and is directed more particularly to a plug so constitutcd as to have longer useful life as well as longer continuous life between overhauls. This is accomplished by making the sparking areas of the electrodes as large as practicable.

The spark gaps of all spark plugs without any exception gradually increase by use due to erosion of the electrode material at the sparking surfaces. The erosion is thought to be due to charged particles or molecules thrown out of the electrodes with each spark. The voltage 1mpressed on the spark plugs and therefore the sparks, being oscillatory in character both the center and the ground electrodes are subject to erosion.

The rate of erosion is aflected by the temperature of the electrodes; the higher the temperature of the electrodes, the higher is the rate of erosion. In the case of aviation engines, especially in the high compression air-cooled types, the erosion is so rapid that frequent resetting of the spark gaps is necessary. Electrodes made of heat-resisting metals resist the erosion somewhat; .however, with the present design of electrodes, the life of spark plugs between overhauls is still considered too short.

Heretofore the electrodes of most of the spark plugs were made in the shape of pins. The tip areas (surfaces perpendicular to the axes of the pin) of the ground electrode against the side of the center electrode, or vice versa, are used as sparking surfaces. have the sparking surfaces of the ground electrodes rectangular in shape. None of them, however, possesses suflicient sparking area to give the desired long life, and, at the same time, have the gaps easily measured and reset.

The primary purpose of the present invention is to produce spark .plugs possessing sumcient long life as to require no attention and no resetting of the spark gaps before the engine in which they are used is ready for overhaul.

The longer life of the subject plug is obtained by making the sparking areas of the electrodes much larger than it has been the practice heretofore. The center electrode of this plug is made conical in shape and the sparking area of the ground electrodes is shapedto conform to the contour of the cone of the center electrode. The sparking areas of the electrodes are limited only by the lateral surface of the center electrode,

as shown in Figs. 1 to 3.

Features of the invention, other than those adverted to, will be apparent from the herein-' Some of the spark plugs 9, 1933, Serial No. sssnio after detailed description and claims when used in conjunction with the accompanying drawing.

The accompanying drawing illustrates the practical embodiment of the invention but the construction therein shown is to be understood as illustrative only, and not definitive of the limit of the invention.

Figure 1 is a cross section of a spark plug showing one form embodying the present invention.

Figs. 2 and 3 show the preferred form in which the full length of the conical surface of the center electrode is utilized for sparking and the cup is cut out into four wide prongs.

Figs. 4 and 5 illustrate a modification in which a long and narrow form of ground electrode is used with the conical center electrode.

Figs. 6 and 7 show a somewhat wider form of ground electrode.

The plug structure of this invention may be included in any conventional plug construction so far as the porcelain, mica, or basic structure is concerned. However, for the. purpose of illustratlon, I have shown the same in the drawing as incorporated in a well known spark plug of the aviation type.

In the accompanying drawing, 5 designates the shell of the plug, provided with various types of ground electrodes. 8 designates the spindle head which has been referred to as the center electrode. It is shown as a frustum of a cone in shape with more or less flattened vertex. This shape ofiers a large sparking area and facility for inspection and adjustment of spark gaps.

Z is the preferred form of the side or the ground electrode. It may be made like a cup with a hole in the middle to receive the center electrode. The curvature of the depression of the cup is identical with that of the center electrode, so that the distances (spark gaps) between any sparking point on the cone of the side electrode and its corresponding point on the center electrode are practically equal. The lateral height of the cone of the side electrode may be equal to, greater than or smaller than that of the center electrode cone. This invention may be carried out in practice by several forms of ground electrodes, some 'of which are enumerated hereafter; for example:

A. As acup as shown in Fig. 1 of any desired depth or height. 7

B. As -a cup cut out to form four wide prongs orleaves as shown in Figs. 2 and 3.

C. .As a bar, rectangular or round .and attached to the shell in any suitable manner as shown e. g. in Figs. 4 and 5, there being one or more of these bars used in a plug.

D. As a part of a cup in the form of 9. prong or leaf as shown in Figs. 6 and 7, there being one or more of these leaves serving as side or ground electrodes.

When a plug, constructed in accordance with this invention is firing in an engine the spark first is' across the smallest distance between the center electrode and the side electrodes following the path of least resistance. The spark continues in this path until the gap resistance of this path, due to process of erosion, becomes larger than that of another path. The spark will then jump across the least resistance again. This process will continue until all the possible proper spark gaps have higher resistance than that of some parasitic gap either in the plug or in the ignition system. The plug will then become inoperative. The plugs will then have to be taken out and the proper spark gaps reset closer to desired value.

The resetting of the proper spark gaps is accomplished by a tool specially constructed for the purpose. This tool pushes the side electrodes inwardly over the center electrodes to the desired amount to produce the proper gap distance. In the case of the solid cup form, the electrode is pressed to the desire depth in a tight fitting bore of the spark plug shell, whereas in the case of the bar or leaf forms of electrodes, they may be bent near their base to properly space them from the center electrode.

On account of the large area of sparking surfaces a much longer service is obtained from this plug with each setting of the gap than from plugs with conventional electrodes.

The lateral surface of a cone is not the largest surface obtainable. A spherical surface, concave, or convex, will give larger area. The inspection of the spark gaps, however, or resetting of the gaps with desired precision will be very difficult with the spherical gaps while with the cone shape no difficulty will be experienced.

The plug of the present invention in any of the ways which I have described it has proven to operate with marked efficiency as compared with plugs designed in accordance with prior practices. It possesses unusually long life. The life of the plug of this construction on the average is three times the life of the plugs with conventional type of electrodes. These plugs have proven to possess such a long life that they required no attention before the engine in which they were operating was ready for overhauling.

In the accompanying drawing, I have illustrated the preferred form, and its variations, of the present invention. Having thus fully described the invention, what I claim as new and desire to secure by Letters Patent is:

1. A spark plug with electrodes having a large area of sparking surfaces composed of a center electrode having a surface, the intersection of which with any plane passed thru the axis of the plug is a straight line, and a side electrode having a similar surface spaced from the first surface a distance substantially equal to the desired spark gap.

2. In a spark plug, a centre electrode having a frusto-conical head; a ground electrode bar attached to the spark plug shell opposite the base of the head and extending therefrom toward the head to a distance equivalent to the spark gap from the surface of the head, from where it extends in a straight line parallel to the surface of the conical head.

3. A spark plug having a shell, a central electrode with a cone shaped head having a sparking surface, the intersection of which with any plane extending longitudinally of said central electrode head through the axis thereof is a straight line, and a set of stout prongs united with the lower end of the shell and constituting grounded electrodes, said prongs having sparking surfaces lying opposite the sparking surface of the central electrode head, and being so formed that the intersection of any of said surfaces with any plane passing longitudinally of said central electrode head through the axis thereof is also a straight line, so that there is a deep and large spark gap surface area between the central and grounded electrodes, which said gap may easily and accurately be measured by a narrow strip or wire gauge feelers, with a large section in the grounded electrodes to carry 01f heat into the shell, the grounded electrodes being adjustable by deflecting their down turned portions inward, so that in such adjustment the large spark gap surface area may be maintained.

4. A spark plug having a shell, a central electrode with a cone shaped head having a sparking surface, a set of stout prongs united with the lower end of the shell and constituting grounded electrodes, said prongs having sparking surfaces lying opposite'the sparking surface of the central electrode head, the intersection of the said sparking surfaces of the central electrode head and the grounded electrodes, respectively, with any plane passing longitudinally of said central electrode head through the axis thereof being parallel straight lines, so that there is a deep and large spark gap surface area between the central and grounded electrodes, which said gap may easily and accurately be measured by a narrow strip or wire gauge feelers, with a large section in the grounded electrodes to carry off heat into the shell, the grounded electrodes being adjustable by deflecting their down turned portions inward, so that in such adjustment the large spark gap surface area may be maintained.

ARMEN A. KASARJIAN. 

